1. Field of the Invention
The present invention relates to an improvement in a magneto-optical recording medium.
2. Description of the Prior Art
In general, a magneto-optical recording medium comprises a non-magnetic substrate, and the substrate holds thereon a layer of an amorphous rare-earth-transition-metal alloy. The layer has the uniaxial magnetic anisotropy perpendicular to a layer face thereof. The layer comprises two to three components, each belonging to transition metals or rare-earth metals.
In the above-mentioned magneto-optical recording medium, a recording operation and a reading operation are performed as follows. In an example case, an amorphous alloy layer is partially heated by a laser beam carefully focused thereon to raise the temperature of the amorphous layer over a compensation temperature of the amorphous layers or over the Curie temperature thereof, and at the same time, an external magnetic field is applied to the layer face perpendicularly thereto. Then, in a heated area, the desired magnetization perpendicular to the layer face is realized. In case a coercive force after cooling down the heated area is enough to stabilize an area which should be magnetically modified for recording operation, a diameter of a stable area can be formed as small as about 1 micron. Information values corresponding to logic numbers "1" or "0" are recorded by allocating them along a direction of magnetization in the layer area.
A reading operation is performed by applying a plane-polarized light beam to the layer area, so as to detect a magnetized direction of the layer area utilizing the Faraday effect or the Kerr effect.
But, the above-mentioned conventional magneto-optical recording medium has a shortcoming the Faraday effect or the Kerr effect is not enough to perform the reading operation, and structure of the amorphous substance is so much changed so as to make restoration to its former state difficult at a relatively low temperature, namely deteriorating the characteristics of the magneto-optical recording medium in the crystallization process. Attempts have been made to add boron to improve the crystallization process (i.e. for increasing the crystallization temperature), but an improvement upon the Faraday effect or the Kerr effect has not been realized. On the other hand, bismuth or tin has been added in an attemtp as to improve the Faraday effect or the Kerr effect, but an improvement upon the rise in the crystallization temperature has not been realized. Both the bismuth and the tin are low-melting point metals having the melting points lower than 300.degree. C. When adding such metals, it is expected that the crystallization temperature rather drops. And further, in the case of making the alloy layer by a sputtering method, it is necessary to suppress the target temperature below the melting point of bismuth or tin, and therefore it is difficult to make the alloy layer with a single target electrode.